Trump won Texas 52% to 43%. About 4.5% voted third party or write-in. Lost in the wash from 2016 is this: "Texas was one of the eleven states where Hillary Clinton improved on Barack Obama's performance in 2012.[2]" https://en.wikipedia.org/wiki/2016_United_States_presidential_election_in_Texas
Assuming the "I hate Hillary" phenomenon was just as prevalent in Texas as the rest of the country, that suggests a possible shift of a point or two in Biden's direction with everything else being the same. Now, if you add in the projection that the 1.5 million new voters (the half that vote) break 2-1 for Biden, you get to about a 3 - 4 point differential. A big unknown is how the smaller third party presence will impact the vote.
Significant factors for 2020:
1. The "Hillary factor" is gone
2. Likely drift away from Trump by suburban women
3. Large number of new voters
4. Lesser third-party presence
5. Motivation